Method of producing a compression-moulded plastic part comprising a neck which is equipped with a dispensing orifice

ABSTRACT

A method for the compression molding of a plastic part including a neck which is equipped with an orifice, in which a blank is created and compressed. The part is molded with a neck which is equipped with a top wall including a thin area with a notch, the contour of this thin area defining the orifice, and two zones which can withstand the mechanical stress necessary in order to break the top wall at the notch. One of the two zones is intended to transmit the mechanical stress and the other is used as a support. The section of the notch is slightly inclined in relation to the axis of the neck. After molding, mechanical stress is applied to one part of the top wall, other than the thin area, so that the top wall tears at the notch, thereby producing the dispensing orifice.

This application is a filing under 35 USC 371 of PCT/FR2003/000837 filedMar. 17, 2003.

BACKGROUND OF THE INVENTION

The invention relates to a compression moulding manufacturing method forplastic parts with a neck in which an orifice is formed. These parts areusually receptacles or part of receptacles. The invention is moreparticularly applicable to conditions for high production ratemanufacturing of moulded objects, that usually have an axisymmetric neckdelimiting an approximately circular orifice, for example heads offlexible plastic tubes comprising a neck provided with a dispensingorifice and a shoulder connecting the said neck to a cylindricalflexible skirt. We will use these flexible tube heads to illustrate thisinvention.

In general, a flexible tube is made by assembly of two parts madeseparately; a cylindrical flexible skirt with a given length (typically3 to 5 times the diameter) and a head comprising a neck provided with adispensing orifice and a shoulder connecting the said neck to thecylindrical skirt. The plastic head may be moulded separately and thenwelded onto one end of the skirt, but the head is advantageously mouldedand welded autogenously to the skirt using either an injection mouldingtechnique (FR 1 069 414) or a compression moulding technique for anextruded blank (FR 1 324 471).

In both of these two techniques, the skirt is fitted around a punch, oneof the two ends projecting slightly beyond the end of the punch, thesaid end of the punch acting as a mould for making the inner surface ofthe tube head (inner surface of the shoulder and the neck). A die isused in these two techniques, that comes into contact with the end ofthe punch, the cavity of this die defining the outer surface of theshoulder and the neck. The main difference between these methods is thatin the first case, these tools are firstly pushed firmly into contactwith each other before injection of the plastic material, and in thesecond case compression of an extruded blank is triggered as they movetowards each other.

In French application No. 0103706 deposited on 19 Mar. 2001, theapplicant indicated that a significant increase in production rates (forexample above 250-300 units per minute) could be achieved using thecompression moulding technique. In the context of this Frenchapplication No. 0103706, the applicant presented a workshop for makingflexible tubes in which tube heads were made by compression mouldingusing continuously moved tools, which provided a means of obtainingsignificantly higher production rates under economically acceptableconditions.

In compression moulding, production of the blank and its placement inthe moulding tool creates specific problems for which solutions havebeen described in a large number of patents. But these problems areexacerbated when it is envisaged to use tools that move continuously andsolutions proposed in the past are not suitable for this new constraint.

French application FR 1 324 471 (Karl Mägerle) describes a compressionmoulding method for tube heads in which the lower mould is composed ofthe end of a mandrel and the end of a skirt that is fitted around thismandrel, the end of the said skirt projecting beyond the end of the saidmandrel; the space delimited by the end of the mandrel and theprojecting part of the skirt is fed by injecting plastic materialthrough several uniformly distributed orifices within a nozzle; theplastic material is distributed around a counter punch formed at the endof the mandrel and used to mould the inner part of the neck. Once thenecessary quantity of plastic material has been injected, the nozzle isremoved, the parts of the top mould are brought towards each other byradial displacement, and the plastic material is then compressed bybringing the lower mould towards the upper mould. The jets are uniformlydistributed around the circumference and the material thus poured isdistributed approximately uniformly around the circumference beforecompression is applied. The result is then an approximately uniformthickness around the dispensing orifice.

Applications FR 2 460 772 (Karl Mägerle) and U.S. Pat. No. 4,943,405(AISA) use the idea of compressing the plastic material when it isalready distributed approximately regularly circumferentially. Theseapplications propose a toroidal extruded blank, that is fitted around acentral protuberance connected to one of the mobile parts of the tool.Fitting a toroidal blank around a protuberance authorises bringing thetwo parts of the moulding tool located at the dispensing orifice intocontact with each other before the plastic material of the compressedblank reaches this zone. More precisely, the air gap between these twotool parts is so small that no viscous flow of the plastic material canoccur. Thus, with a toroidal blank, it is easier and more direct toobtain a neck provided with an orifice with a clean edge.

In FR 2 460 772, the toroidal blank is extruded using an extrudingmachine with a ring die opened under the control of a valve. This valvemay or may not close off the annular flow of the plastic materialdepending on its position, and its displacement controls the size of thetoroidal blank thus obtained. The use of toroidal blanks obtained bydiscontinuous extrusion of plastic material controlled using a valve istherefore the only known way in prior art of efficiently and directlyobtaining a neck with an orifice provided with a clean edge, directly bycompression moulding. However, this type of technique is not veryprecise and it cannot give good reproducibility of the weight of atoroidal blank, which complicates compression moulding conditions, forexample compression moulding does not have the same flexibility asinjection moulding, for which all surplus material can easily beevacuated.

Moreover, the toroidal blank is cooled fairly quickly by conduction inthe tooling. Since the contact surface is not uniformly distributed,cooling is heterogeneous and a large proportion of the advantageprovided by the toroidal geometry of the blank, namely good distributionof the material before compression, is lost. Many solutions have beenproposed like that proposed in WO96/09151 (Karl Mägerie Lizenz) toreduce the amplitude and heterogeneity of cooling of the blank beforecompression, but they require the introduction of additional toolingelements (for example the auxiliary support sliding around the centralprotuberance described in WO96/09151) and means of controlling theirdisplacement. This type of sophistication makes this type of tooleconomically unattractive or even prohibitive if it is required to makethe mobile parts of the tooling follow a continuous overall movement.

Finally, production of the toroidal blank and its placement in the airgap between the punch and the die introduce serious difficulties whenthe tools are moved with continuous dynamic movements, since extrusionand injection are not suitable for continuous movement of tools, andtransfer means have to be provided capable of either displacing theextrusion means themselves so that the blank can be obtained, or thetoroidal blank obtained “statically” has to be recovered and placed inthe air gap of the compression tools that move continuously, withoutdeforming it too seriously.

Application EP 0 841 258 describes a compression moulding manufacturingmethod for plastic inserts that are introduced in proportioning caps.These inserts are provided with a cylindrical dispensing spout and havea wall closing off the dispensing orifice, which seems to indicate thatthe blank used is not necessarily toroidal, that it can be solid makingit easier to make, and there are fewer difficulties in depositing it inthe air gap of the tooling. But this wall must be removed after theinsert has been formed by cutting it out using a cutting tool. Thiscutting operation involves a series of additional steps, and althoughthis is possible for fairly small inserts, it is difficult to transposeit to the use of compression moulding for shaping the tube head withautogenous welding of the head onto the skirt, since the toolinginvolved is larger and more complex. The problem becomes even morecomplicated if they are to move along a continuous overall movement.

Therefore, the applicant tried to find a method for the use ofcompression moulding for manufacturing plastic parts provided with aneck with an orifice, that is not affected by the problems mentionedabove and that can consequently be done easily using continuously movingtools.

SUMMARY OF THE INVENTION

The objective of the invention is a compression moulding manufacturingmethod for plastic parts with a neck provided with an orifice,comprising a first step for making a plastic blank and a second step forcompression of the said blank, in which the said blank is brought to anappropriate temperature and is then placed in the air gap between atleast two moving parts of the compression tool and is then compressed bybringing the two mobile parts of the tooling towards each other, theplastic material of the blank flowing so as to fill the cavities in thesaid mobile parts until the said mobile parts stop moving relative toeach other, the cavities of the said mobile parts of the tooling oncebrought together defining the volume of the said part with a neck, thesaid cavities being designed such that the said neck, once moulded, hasa top wall that comprises a thinned zone for which the contour delimitsthe required shape of the orifice, the said method being characterisedin that the said thinned zone is bounded by a notch for which thesection in a diametric plane passing through the axis of the neck isoriented along a direction approximately parallel to the axis of theneck, and in that the said top wall also comprises a zone in which amechanical force is applied that will be applied to the said top wallwith sufficient intensity to break the top wall at the said notch, thesaid application zone being distinct from the thinned zone, the said topwall also including two zones that can resist the said mechanical force,one of them being designed to transmit the said mechanical force and theother to act as a support, and in that after opening the said mouldingtool by relative displacement of its mobile parts, the next step is toapply the said mechanical force in the said application zone such that abreak will occur at the said notch and at least part of the top wall isdetached thus opening up the dispensing orifice.

The said notch has a section in a diametric plane passing through theaxis of the neck oriented in a direction approximately parallel to theaxis of the neck, in the sense that it makes a fairly small angle withthe said axis, typically between 0 and 45° and preferably between 0 and30°.

In the following, we will refer to the thinned zone of the top wall atthe notch as the rupture zone or the breakoff zone. The breakoff zone isthus a part of the thinned top wall, for which one of the faces isprovided with a notch. This notch may be on the bottom face of the topwall, but it will preferably be on the top face of the top wall so thatany deformations of the residual thinned zone resulting from the failurewill not create any geometric visible or touchable defects (splinterscausing injury).

The top wall is not necessarily a wall with a constant thickness. It maycomprise different parts, some of which may be solid but it comprises atleast one part that acts as a wall closing off the dispensing orifice.

The moulding tool designed to make the moulded part is conventional; itincludes at least two mobile parts free to move with respect to eachother. In the case of a tube head, these two parts are the punch and thedie. The neck very often needs to have a screw thread on its outer wall,which imposes that a die should be used itself composed of severalmobile parts that move away from each other—for example using radialdisplacements—to facilitate unmoulding of the threaded part.

The moulded part according to the invention has a neck that is initiallyprovided with an orifice; the orifice is made in a subsequent step,without the need to use a cutting tool. Consequently, compression may beachieved using a blank that is not necessarily toroidal, that has asolid shape that is firstly easier to obtain with a reproducible weight(improvement of compression moulding conditions) and secondly reducesthe amplitude and heterogeneity of cooling. This part has betterreproducibility by weight since a solid extrudate can be extruded withshears at the exit from the die; the material quantity thus obtaineddepends on the displacement perpendicular to the extrusion direction ofa shear blade external to the die and not on the displacement of a valvesliding in the axial direction inside the die, and that discontinuouslycloses off a ring orifice.

There is a top wall above the neck that temporarily closes the orificeand part of which (that we will subsequently call the shutter) ispartially or completely detached in a subsequent step in the method byapplying a simple mechanical force to part of the top wall, called theapplication zone of the mechanical force, and distinct from the breakoffzone.

The top wall comprises at least four zones; a zone in which themechanical force is applied, a zone of mechanical force transmission, abreakoff zone and a pressure zone. The mechanical force will be appliedlocally on the said top wall near the application zone, with asufficient intensity to break off the said top wall at the said notch.The intensity of the force necessary to cause breakage depends on thedirection of the said mechanical force and the distance between thepoint of application of this force and the breakoff zone.

In one preferred embodiment, the shutter (in other words the part of thetop wall that is partially or completely detached after the breakoffzone) is the zone that transmits applied forces to tear the top wall atthe notch and the part corresponding to the attachment of the top wallonto the neck is the support zone. The geometry of the shutter isarbitrary provided that it is adapted to the type of mechanical forcethat has to be applied to cause breakage. It may be in the shape of astick to amplify a force applied at its end by the lever effect, asillustrated in FIG. 1, or it may be in the form of a simple wall asillustrated in FIG. 4, or it may be provided with a protuberance forwhich the cross-section is in the shape of a non-convex polygon (FIG. 5)or for which the section (in a diametric plane through the axis) is inthe form of a T shape as shown in FIG. 3. The notch follows an arbitrarycurve, not necessarily plane and not necessarily closed. If it isclosed, breakage of the breakoff zone causes complete detachment of theshutter. This shutter can advantageously be taken out, preferably usingthe residual part of the energy provided to break the breakoff zone. Thenotch may also have an open contour. In this case, breakage of thebreakoff zone causes partial detachment of the shutter. The shutter isthen in the form of a tongue that must be held folded in an openposition such that the orifice is delimited by the contour of the brokenbreakoff zone and the bottom of the tongue thus obtained and heldfolded. In the latter case, there is no need to remove the partiallydetached shutter.

A notch is formed in the breakoff zone, for which the section in adiametric plane passing through the axis of the neck is oriented along adirection that is only slightly inclined with respect to the axis of theneck. For example, if the notch is V-shaped, the bisecting line of the Vis only slightly inclined with respect to the axis of the neck and is inthe shape of a cylinder or a cone with an angle at the centre of lessthan 90°, and preferably less than 60°. Thus, the said bisecting lineforms an angle of between 0 and 45°, and preferably between 0 and 30°,with the axis of the said neck. The angle of the V is between 30 and90°, typically between 40 and 50°. The V does not necessarily have itsarms symmetrical about its bisecting line.

In general, the required orifice is simply circular and the breakoffzone is a ring notch for which the cross-section is a V for which theinternal arm (in other words the arm closest to the axis) is slightlyinclined with respect to the axis and for which the external arm is morestrongly inclined. Typically, the internal branch of the V forms anangle of less than 5° with the axis, the bisecting line is at an angleof 25° with the axis of the neck and the angle between the outside armand the axis of the neck is less than 55°.

The shape of the notch locally enables concentration of stressesgenerated by the application of a mechanical force, regardless ofwhether it is a force or a moment applied at a particular location onthe shutter. The transverse wall may be small, for example limited tothe breakoff zone, but it must be present to orient the notch such thatits axis is approximately parallel to the axis of the neck.

The applicant has observed that this type of geometry concentrates thebreakage energy and tolerates a large number of mechanical stresses thatcan cause controlled tearing of the breakoff zone. This tolerance ismuch greater than with a ring notch, for example located on the wall ofthe neck and which has a section (in an axial diametric plane) in theshape of a V for which the bisecting line is perpendicular to the axisof the neck.

Due to the presence of the notch, the easily breakoff zone is thinnerthan the neighbouring zones. Preferably, the residual thickness underthe notch is 30% less than the global thickness of the transverse walloutside the notch. Typically, for the envisaged receptacle geometries,it is between 0.1 and 0.6 mm. Since it is thin, it cools more quicklythan other parts of the neck, so that forces causing breakage can beapplied without necessarily applying shocks, in other words applyingforces causing deformation rates of the order of 10³ s⁻¹. The mechanicalforce may for example be an axial thrust or tension, rotation about theaxis of the neck, a combination of the two (for example duringunscrewing—stripping the head), a force applied on the other end of thestick-shaped shutter, etc.

In one preferred embodiment of the invention, the shutter breaks duringcooling after moulding, as soon as the material stabilises, whichprovides a means of breaking the shutter before the part is ejectedoutside the moulding tool. It is recommended that the breakoff zoneshould be broken as soon as the temperature of the plastic materialbecomes close to its vitreous transition temperature in the saidbreakoff zone, or otherwise wait until the entire head has cooled, thetemperature of the breakoff zone increasing as the moulded part coolsdue the thermal inertia of the thicker zones surrounding it.

It is also advantageous to place the blank to be compression mouldedabove or directly facing the end of the protuberant part of the mouldingtool that will be used to make the inner surface of the neck. The partof the blank that is in contact with the tool cools slightly faster thanthe rest of the blank by conduction. Surface imperfections related tothe increased cooling of the plastic material at this location, tofriction and the resulting heterogeneous material flow, will remain onthe shutter that will then be detached. Therefore, they will not bevisible.

This method is particularly advantageous when continuously movingmoulding tools are used, like those described in French application No.01 03706 deposited by the applicant on Mar. 19 2001. In thisapplication, apart from the fact that movement towards each other willcause compression of a blank, moulding tools are also moved by acontinuous general movement with a component that is not necessarilyplane but that remains orthogonal to the direction along which they movetowards each other. Example 2 described below illustrates an embodimentof the invention applied firstly to production and placement of blankson continuously moving moulding tools, and secondly to making theorifice while the moulded tube head is still inserted on the movingpunch.

Another solution applicable for a continuously moving system consists ofmaking part of the shutter in the shape of a stick similar to the shapein example 1 and applying a force at the end of the stick as soon as thedie has moved away from the punch, for example using a fixed pin infront of which the punch still fitted with the tube head moves. Underthe effect of bending imposed on the stick and transmitted by the stickto the transverse wall, the breakoff zone breaks and the shutter isejected along a precise and reproducible direction away from thenon-stop manufacturing line.

To obtain a clear and reproducible break, the modulus of elasticity ofthe material in tension at room temperature is preferably more than 200MPa, and preferably more than 500 MPa.

Although this method was developed for non-stop manufacturing of mouldedparts with a neck containing an orifice, it may also be applied tomoulding methods in which machines are working on individual parts. Dueto the design of the breakoff zone involved, the method according to theinvention is used to choose, among a large number of possible mechanicalforces, the mechanical force to obtain a controlled tear offing of thebreakoff zone at lower cost.

The final step in the method in which the shutter is torn off, may beincluded in the actual manufacturing (used during cooling and aftermoulding, or immediately before being removed from the non-stopmanufacturing line, etc.). It may also be delayed until the first use;example 5 illustrates this case, in which the user activates the shutterbreak mechanism when he unscrews the stopper for the first time. Thisembodiment of the invention can result in tube heads provided with asystem guaranteeing that the tube has not been violated before it wasused for the first time.

BRIEF DESCRIPTION OF THE DRAWINGS

The set of Figures illustrates the manufacture of flexible tubes. Apartfrom FIG. 3, they show diametric sections through tube heads, parts ofthe compression moulding tool, or caps.

FIG. 1 a shows a particular tube head made according to the invention,before the force necessary to break the breakoff zone is applied.

FIG. 1 b shows a particular shape of the section through the breakoffzone according to the invention.

FIG. 2 a shows a diametric section showing placement of a blank in acompression moulding tool.

FIG. 2 b shows the moulding tool and the moulded part at the end ofcompression. The moulded part has a T-shaped shutter so that there is aring groove on the outer surface of the shutter.

FIG. 2 c shows separation of the punch provided with the head of thetube thus moulded. The ring notch is not shown, due to the scale used.

FIG. 2 d shows elimination of the shutter after the breakoff zone hasbeen broken off, caused by the axial displacement imposed by a fork, theprongs of which are engaged in the ring groove.

FIG. 3 shows a perspective view of a solution in which the tubes inFIGS. 2 a to 2 d are made using moulding tools that follow a continuousrotation movement and during this rotation, the shutters are simplyremoved by the ends of the said mobile shutters being trapped in astatic rail that is not tangent to the trajectory of the tubes.

FIG. 4 shows another case in which the shutter is torn off and is thenremoved by applying an axial thrust.

FIG. 5 shows another case in which the shutter is torn off and thenremoved using an unscrewing movement during stripping from the die.

FIG. 6 shows three variants of an embodiment of the invention in whichthe neck is insert moulded by compression on a stopper that waspreviously placed in a cavity of the die. FIG. 6 a shows the devicebefore compression insert moulding of the tube head on the cap; FIG. 6 bshows the device after compression insert moulding of the tube head onthe cap; FIGS. 6 c), 6 e) and 6 g) illustrate parts of the toolingprovided with the toroidal edge that forms the breakoff zone (6 c): thepunch shown in 6 e), and the stopper shown in 6 g); FIGS. 6 d), 6 f) and6 h) show details of the assembly of the tube head+stopper obtainedafter insert moulding in three different cases.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 (FIGS. 1 a and 1 b)

Tube Head Designed Within the Context of the Method According to theInvention

The tube head 1 illustrated in FIG. 1 a shows a shoulder 2 and a neck 3in which there is a top wall 4 above the top end, the top wall includingat least one thinned zone 6 for which the upper face is provided with anotch 5 for which the closed contour delimits the required shape of theorifice. This thinned zone 6, also called the breakoff zone, issurrounded by two zones 7 and 8 capable of resisting the mechanicalforce F necessary to break the said breakoff zone, one of them (7) beingintended to transmit the said mechanical force and the other (8) to actas a thrust application zone.

The shutter 14 is the part of the top wall 4 that is detached, and inthis case removed by application of the mechanical force F on the end 91of the stick 9. The force application zone is end 91 of stick 9. Thezone that will transmit the mechanical force includes the stick 9 andthe wall 7. Application of the mechanical force F amplified by theeffect of the lever arm formed by the stick 9, has the consequence ofbreaking the breakoff zone and evacuating the said shutter 14.

The breakoff zone 6 is notched with a V-shaped notch 5, with an innerarm 61 that forms an angle of 5° with the axis of the neck, an externalarm 62 that forms an angle of 55° with the said axis, and the bisectingline 63 of the V that forms an angle of 25° with the axis of the neck.

In the special case of this example, the head is moulded with highdensity polyethylene. Its neck 3 has an outer diameter of 11.5 mm and anaverage thickness of 1.5 mm (excluding the screwing thread). Thetransverse wall 7 is approximately 1 mm thick, and is connected to thetop end 8 of the neck 3 that acts as a support zone. The height of thestick 9 is 10 mm, the residual thickness of the wall at the breakoffzone is 0.3 mm.

All that is necessary is to apply a force F equal to approximately 1Newton, to tear the breakoff zone so that the shutter will be ejected.Once the shutter has been removed, there is a 7 mm diameter orifice inneck 3 that is free from any runs or local deformation.

If continuous moving moulding tools are used as in example 2, the punchon which the head 1 of the tube is fitted moves in front of a fixed pin,as soon as the die moves away. This fixed pin retains the end 91 of themoving stick 9, and under the effect of the bending imposed on the stickand transmitted through the stick to the transverse wall 5, the breakoffzone 6 breaks off and the shutter is ejected along a precise andreproducible direction away from the continuously moving productionline. The applicant obtained clean and sharp cuts in the breakoff zonewith a linear velocity equal to or more than approximately 0.2 metersper second. Very satisfactory results were obtained at a velocity of 0.8meters per second with heads moulded with high density polyethylene.

Example 2 (FIGS. 2 a, 2 b, 2 c, 2 d and 3)

Method According to the Invention Applicable to a Continuously MovingMethod of Making Tube Heads by Compression Moulding

The flexible tube is made by assembly of two parts made separately; acylindrical flexible skirt 10 and a head similar to that describedpreviously. The high density polyethylene head is moulded andautogenously welded onto an end 11 of the skirt 10, using a compressionmoulding technique for an extruded blank 20.

FIG. 2 a shows a diametric sectional view of the placement of a highdensity polyethylene blank 20 in a compression moulding tool. Thismoulding tool comprises a punch assembly 35 and a die assembly 30.Compression is obtained by reducing the distance between the punchassembly 35 and the die assembly 30 until the two parts of the toolingare relatively immobilised. Each of these parts of the tooling comprisesparts (350 and 351, 300 and 301 respectively) that may be free to movewith respect to each other, but which are fixed together during thecompression. Relative displacement of these parts does not require theaddition of any special control; it is controlled by the overallrelative movement between the punch assembly and the die assembly. Atthe beginning of compression, the central protuberance 352 is fixed tothe peripheral part 351 to form the punch assembly 35. The parts 300become adjacent following a radial displacement imposed by a conicalinsertion, and the assembly fixed to the upper part 301 forms the dieassembly 30.

The skirt 10 fits around the peripheral part 35 of the punch, one of itsends 11 projecting slightly beyond the end of this part 35 of the punch,which acts as a mould for making the inner surface of the tube head(inner surface the shoulder and the neck). The end 352 of the centralpart 350 of the punch is a central protuberance designed to mould theinside of the neck. The mobile parts 30 of the die move in the radialdirection to free the screw thread once it has been moulded.

FIG. 2 b shows the moulding tool and the moulded part 21 at the end ofcompression; it is a flexible tube 21 including the cylindrical skirt10, the shoulder 22 and the neck 23 on which a top wall 24 is fitted.The head was moulded and autogenously welded onto the end 11 of theskirt 10. The top wall 24 comprises a transverse wall 25 acting as ashutter closing off the dispensing orifice and a protuberance 29 with aT-shaped section, such that it comprises a ring groove 28 on its lateralwall.

FIG. 2 c shows the separation movement of the punch assembly from thedie assembly. The flexible tube thus made remains fixed to the punchassembly and cools. A fork 40 is moved close to the tube head after afew seconds of cooling when the high density polyethylene hasstabilised.

FIG. 2 d shows evacuation of the top wall 24 after breakage of thebreakoff zone, which was caused by the axial displacement imposed by thefork 40, the prongs of which are engaged in the ring groove 28. Thegeometry of the breakoff zone 26 with its ring V-shaped notch isidentical to the geometry of the breakoff zone in example 1. In thisway, the head of the finished tube 50 has a cylindrical neck providedwith a dispensing orifice.

FIG. 3 shows an alternative solution to that shown in FIG. 2 d; mouldingtools, and particularly punches, follow a continuous rotation movement Rlike that imposed by the device reference 10 in FIG. 2 in Frenchapplication No. 01 03706. Once formed, the tubes 50 remain fixed to thesaid punches after moulding, and shutters are removed simply by trappingthe ends of the T-shaped shutters, their ring grooves 28 being engagedin a static rail 40′ not tangent to the trajectory of the tube heads.

Example 3 (FIG. 4)

FIG. 4 illustrates another method of production of the tube in which thehead is also compression moulded and simultaneously welded onto theskirt, in which the top part 64 comprises a simple wall 65 with a ringnotch close to its attachment onto the neck. The wall is torn off andthen removed using an axial thrust. As illustrated in FIG. 4, thegeometry of the shutter may be limited to the wall 65 or as illustratedin FIG. 1, it may include the said wall and also be provided with astick shaped part to facilitate gripping and applying the axial thrust.

Example 4 (FIG. 5)

FIG. 5 illustrates another case of production of the tube in which thehead is also compression moulded and welded simultaneously onto theskirt, in which the top wall 74 includes a protuberance 75 with anon-convex polygonal section (typically a star) and a bottom part actingas a shutter. The die 30′ does not contain any radially moving parts(300) and the head with its threaded neck is unmoulded by unscrewing.Since the non-convex polygonal protuberance 75 still occupies the cavityof the mould in which it was formed, it is prevented from rotating, thebreakoff zone tears off under the effect of the resulting torsion, theprotuberance is thus detached and removed during unscrewing.

This type of shutter can also be made on dies with parts that move inthe radial direction (300). In this case, the tube head is unmouldedafter cooling and the break off zone is then torn off and the shutter isremoved by rotation using a key with a shape complementary to the shapeof the concave polygonal section.

Example 5 (FIGS. 6 a to 6 h)

This example solves the difficult problem imposed by the extremely finesetting of the air gap existing at the end of travel distance betweenthe mobile parts of the tool, particularly close to the cavity used toshape the breakoff zone. To obtain uniform breakage conditions on thesetubes made at high production rate, it is important that the geometry ofthe breakoff zone should be as repeatable as possible, and its minimumthickness must not vary by more than a few hundredths of a millimeter.

It takes a long time to make this difficult setting of the air gap,which limits the production rate, particularly because it has to be donefrequently (setting changes due to tool expansion, wear of active parts,etc.). Furthermore, there is a serious risk of tool breakage if there isa setting fault, lack of plastic material in the tooling, presence of aforeign body, etc. Finally, there is also an increased risk of anendurance defect in the tool due to its sensitivity to wear.

These various points are advantageously reduced if not entirelyeliminated if the breakoff zone is formed by compression moulding of ablank between a rigid metallic element (for example belonging to thepunch) and a less rigid element, for example made of plastic. Thus, acompression tool with a first mobile part and a second mobile part isused, the said first mobile part being made of a material that is lessrigid than the material used for the said second mobile part, at leastin part of the cavity contributing to shaping of the said breakoff zone.This may advantageously be achieved if this part of the neck is insertmoulded directly on the stopper that will close off the dispensingorifice.

The association of two materials (one metallic, the other plastic)enables contact between two moulding parts without any risk of damage toeither of the parts. The adjustment fineness of the air gap can thus belimited (reduction of the setting time), reducing the risk of damage totools (mechanical stop on the cap, or tooling stop on the shoulder inthe case of a stopper presence fault). Moreover, due to insert moulding,a receptacle plus stopper assembly is obtained directly in which thecontact surfaces correspond to each other perfectly which enableshermetic closing of the receptacle throughout its usage duration.

Thus, in the context of this embodiment of the invention, one of themoving parts of the tooling (the die) may be provided with a stopperthat will close off the said orifice. This stopper is positioned so thatits inner surface acts partially as a moulding cavity to shape the saidneck, at least at its breakoff zone.

The neck can be insert moulded on the stopper in a manner similar to themethod described in example 4 in international applicationPCT/FR02/00686 deposited by the applicant. The objective in this methodis to make a flexible tube. The tube head is moulded and welded to acylindrical skirt obtained by cutting out from a sleeve. In this specialcase, the head is welded to the skirt at the same time as it is shaped.

FIG. 6 a shows a stopper 805 that is placed in the cavity of the die830. As indicated in international application PCT/FR02/00686, thisstopper may itself have been moulded shortly before, using the same die,but it is also possible that it was obtained independently on anothermoulding device. Outside this cavity, the shape of the cavity in the die830 defines the outer surface of the shoulder 82 of the tube. The innersurface of the stopper 805 defines the inner surface of the neck 83 andthe bottom of the neck.

The punch 835 is provided with a skirt 801 for which the end 802slightly projects beyond the shoulder 846 of the punch. The averagethickness of this stopper 805 is 1 mm. The inner surface of the cap,possibly provided with one or several screw threads, defines the outersurface of the neck to be formed. The part of the cavity of the die 830that is not covered by the stopper defines the outer surface of theshoulder. The die 830 acts as a support tool.

A low density polyethylene blank 820 taken at the exit from the extruderis deposited either on the end of the punch or in the cavity of the die820. It is compressed by bringing the punch and die towards each otheruntil the screwed shape of the head is obtained. Under the effect ofthis translation, the blank 820 is deformed and flow of the plasticmaterial is guided by free surfaces of the residual air gap thatprogressively reduces the volume. When the punch 835 and the die 830touch each other, they define a moulding cavity in which the end 802 ofthe skirt is trapped. Under the effect of compression, the plasticmaterial of the blank flows and fills in the various parts of the volumedelimited by the cavities of the punch and the die, thus forming theshoulder 82 and the neck 83 provided with a top transverse wall 84 and abreakoff zone 86. The plastic material also comes into contact with theend 802 of the skirt. The plastic materials used in the head and theskirt are intimately welded together without any addition of heat ormaterial. They remain welded together after keeping under low pressureand after cooling.

The tools are moved apart and the assembly is extracted. The assembly isallowed to cool to enable complete dimensional stabilisation of the neckand the cap.

The breakoff zone (86, 86′, 86″) is formed using a moulding part that isprovided with a toroidal-shaped edge (90, 90′, 90″). This toroidal edgebelongs either to the male tool (punch—FIG. 6 c)-90), or to the stopper(FIG. 6 e) (90′) and FIG. 6 g (90″)). In the first case (FIG. 6 c) and 6d)), the break takes place on the outer surface, but there is a smallrisk of a run appearing because the steel toroidal edge makes itpossible to impose sharp angles, therefore with a high multiplicationfactor on stresses occurring in the breakoff zone during rupture. Inother cases, a run that might result from breakage of the breakoff zonemay remain unseen inside the neck.

The breakoff element may be fixed to the cap, by including a reversetapered protuberance 89 or 89′ on the cap. The tube will only beactually opened the first time that the stopper is unscrewed and thebreakage force could then be considered as a non-violability system.

A slight relief such as a rice grain can be provided at the end of thescrewing thread, in order to prevent the stopper from being unscrewedafter the head has been formed. The reverse tapered protuberance canpass through the thickness of the stopper (89″) and the material thusextruded through the stopper may be used to fill the top of the stopperand particularly to form a personalised decor, for example a customerlogo.

Advantages

-   -   simple moulding tool;    -   elimination of defects associated with previous methods of        making the orifice (runs, pollution, seizure, etc.);    -   better reproducibility of the blank in terms of weight which        improves the reliability of compression moulding;    -   easily adapted to a non-stop manufacturing method.

1. Compression molding method using continuously moving tools formanufacturing plastic parts having a neck provided with an orifice,comprising the steps of: bringing the blank to an appropriatetemperature, and then placing the blank in an air gap between at leasttwo moving parts of a compression molding tool and bringing the at leasttwo moving parts towards each other to compress the blank, the plasticmaterial of the blank being caused thereby to flow so as to fillcavities in the moving parts until the moving parts stop moving relativeto each other, the cavities once brought towards each other defining avolume of the part with a neck, constructing the compression tool toproduce a molded neck having a top wall that comprises a thinned zonehaving a contour that delimits a shape of the orifice, the compressiontool being constructed such that the thinned zone is bounded by a notchhaving section in a diametric plane passing through the axis of the neckwhich is oriented along a direction approximately parallel to the axisof the neck, and such that the top wall also comprises a breakoff zonein which a mechanical force can be applied to the top wall withsufficient intensity to break the top wall at the notch, the applicationzone being distinct from the thinned zone, the compression tool furtherbeing constructed such that the top wall also includes two zones thatcan resist the mechanical force, one of the zones being designed totransmit the mechanical force and the other of the zones acting as asupport, a protuberance extending from the top wall parallel to the axisof the neck, and opening the molding tool by relative displacement ofthe moving parts, during which a moving part of the molding tool appliesa bending force to the protuberance sufficient to cause a break to occurat the notch and detach at a wall of the top wall.
 2. Method accordingto claim 1, wherein the breakoff zone breaks during cooling aftermolding, under a force applied as soon as the temperature of the plasticmaterial becomes close to a vitreous transition temperature in thebreakoff zone.
 3. Process according to claim 1, wherein the breakoffzone comprises a V-shape notch, the V having an angle of between 30 and90°, and having a bisecting line forming an angle of between 0 and 45°with the axis of the neck.
 4. Method according to claim 1, wherein thetop wall comprises a transverse wall and a stick having an end at whicha force can be is applied laterally to cause breakage of the breakoffzone.
 5. Method according to claim 1, wherein the top wall comprises atransverse wall acting as a shutter and a protuberance with a T-shapedprofile, forming a ring groove on an outer surface thereof, in whichprongs of a fork or a rail may be engaged, with relative displacementcausing tearing off and then removal of the shutter.
 6. Method accordingto claim 1, wherein the parts of the compression molding tool are alsomoved by a continuous movement orthogonal to the direction along whichthe parts move towards each other.
 7. Method according to claim 1,wherein the compression molding tool comprises a first moving part and asecond moving part, the first moving part, at least in a part of thecavity used for shaping the said breakoff zone, being made of a materialthat is less rigid than a material used for the second moving part. 8.Method according to claim 7, wherein the first moving part is made ofplastic material, at least in the cavity part used for shaping thebreakoff zone, and the second moving part is metallic.
 9. Methodaccording to claim 8, wherein the first moving part comprises a cavityprovided with a stopper to close off the orifice, the stopper beingpositioned such that an inner surface thereof acts partially as amolding cavity for shaping the neck, at least at the breakoff zone. 10.Process according to claim 9, wherein the breakoff zone is shaped usinga part of the stopper which forms a toroidal edge.
 11. Process accordingto claim 7, wherein the breakoff zone is shaped by a moving part portionforming a toroidal edge.